Five thousand concrete arch segments for the 2.5km Chipping Warden tunnel are being aligned in the excavated alignment and will then be covered with earth and vegetation to hide them.
Chipping Warden is one of five so-called ‘green tunnels’ that are being built on phase one of the HS2 project between London and Birmingham.
The technique has been imported from France by Eiffage, a quarter of the EKFB main works contracting joint venture, along with Kier, Ferrovial and Bam Nuttall. The tunnel segments are being made by Stanton Precast in Ilkeston, Derbyshire.
Designed as an m-shaped double arch, the tunnel will have separate halves for southbound and northbound trains. Instead of casting the whole tunnel on site, five different concrete precast segments are slotted together to achieve the double arch – one central pier, two side walls and two roof slabs. All 5,020 segments will be steel reinforced, with the largest weighing up to 43 tonnes.
EKFB project manager Jeremie Martin said: “Seeing the first set of precast units being installed is a milestone that the whole team is very proud of. This three-year construction programme will benefit from off-site manufacturing making the green tunnel build more efficient than the traditional on-site building method.
“The HS2 green tunnels are a first of its kind in the UK. We have designed them as a twin arch ‘M’ shape which is more efficient than the standard box structure, reducing the amount of concrete required, which is a great example of how innovative engineering design can reduce carbon impact.”
The tunnel will be built in sections, with construction expected to be complete in 2024.
Similar green tunnels will also be built at nearby Greatworth as well as in Wendover (Buckinghamshire) and Burton Green (Warwickshire. The tunnels will all have ‘porous portals’ at either end to dampen the noise of trains entering and exiting the tunnel, along with portal buildings to house safety and electrical equipment.
Tailored landscaping will be developed for each tunnel, with native trees and shrubs typical to the local area such as Silver Birch, Oak, Beech and Willow planted to create new woodland areas around the portals and recreate the hedgerows and field boundaries on top of the tunnel.
All 13,290 segments for Chipping Warden, Greatworth and Wendover are being made by Stanton Precast.